Fuel pump arrangements



Jan. 24, 1961 s R. TYLER FUEL PUMP ARRANGEMENTS Filed May 20, 1958 f! R Q l/vmvrae STA/v16 V RALPH r1462 5 M *6 ,4 r rue/vs xi United States PatentO FUEL PUMP ARRANGEMENTS Stanley Ralph Tyler, Cheltenham, England, assignor to Dowty Fuel Systems Limited, Cheltenham, England Filed May 20, 1958, Ser. No. 736,539

'Claims priority, application Great Britain May 22, 1957 Claims. (Cl. 103-161) This invention relates to fuel pump arrangements intended particularly for use with aircraft engines. The object of the invention is to provide a double pump arrangement in a liquid supply system, such as the fuel supply system of an aircraft, to reduce the possibility of pump failure, and a single control which normally acts on both pumps, but which during failure of either pump can equally well act on the serviceable pump alone. The references hereinafter to a fuel system, or to fuel pumps, are to be taken as comprising the broader conception noted above.

In accordance with the present invention, a fuel pump arrangement comprises a pair of variable delivery pumps having their outlets connected together, or both to a common delivery duct, a lever pivotally interconnecting the displacement controls of the two pumps, a fulcrum for the lever at a position between its connections to the displacement controls, the lever being arranged to be movable on application of a predetermined operating force, and a control means for the pumps which acts to rock the lever angularly about this fulcrum to increase or decrease the pump displacements simultaneously whereby if one displacement control becomes fixed then movement of the lever by the control means will result in movement of the fulcrum so that the other displacement control can be moved to obtain the desired variation in fuel flow. In the event that one pump fails and its displacement control is not fixed in position then the control means will operate to control fuel output by movement of the displacement control of the remaining pump the lever fulcrum remaining fixed. It is preferred that the individual outputs of each pump, which normally are additive, should pass through non-return valves before being connected together to prevent the output of one pump passing through the other pump if the latter is disabled. Also, the mechanical drive to each pump should be frangible so that if a pump becomes seized the drive will break.

One example of the invention will be described with reference to the accompanying drawings, wherein Figure 1 is a diagrammatic isometric showing of the invention, and Figure 2 is a diagram of the hydraulic relationship between two such paired pumps.

In this embodiment of the invention a pair of variable displacement fuel pumps 1 and 2 is provided side by side, both being driven through separate shafts, each of which includes a shear neck It: or 2a which will break on application of excessive torque. Each pump is, for example, of the radial rotating cylinder block type which includes a track ring respectively 3 and 4 of variable eccentricity disposed around the corresponding cy'inder block 5 or 6 and engaged by slippers respectively 7 and 8 which reciprocate pistons within the cylinders radially arranged in the cylinder blocks. Each track ring constitutes a displacement control for its pump. They are pivotally mounted at an external position respectively 9 and 11 so that eccentricity variation is obtained by pivotal movement of the track ring. At a position on each track ring diametrically opposite to the pivot, a ball-ended member respectively 12 and 13 extends. A lever 14 to act upon the displacement control, extends between these ball members and engages on them by means of forked ends 15 and 16 or in any other suitable manner. The centre of the lever 14 is located by a pivot 17 which is carried in the bifurcated end 18 of a rod 19. The rod 19 is slidably mounted in a housing 21 and extends in a direction substantially perpendicular to the mean position of the lever 14. The remote end of this rod includes a head 22 which is engaged on each side by leaf springs, 23, each tensioned to a predetermined load and located by stops 24 at the normal position of the rod, such that the rod may be displaced axially in one direction or the other, and in the plane in which the lever 14 rocks, only by the application of a force which exceeds the tension of one or other of the leaf springs 23.

For angular movement of the lever an extension 25 from its centre is provided, this extension being in a direction generally perpendicular to the lever itself. The remote end of this extension 25 is connected through a pivoted link 26 to a servo piston 27 so that movement of the latter within its cylinder 29 will result in angular movement of the lever 14. The servo piston is doubleacting and controlled in any suitable manner, as by the normal type of spool control valve 28. Alternatively, it may be controlled on one face by a pressure governed by a servo vent so that increase in pressure will move the track rings to one limit of movement, a return spring being provided to move the lever, the servo piston and the track ring to the other limit of movement. A further alternative is to arrange control by a differential area servo piston controlled in the usual way by a servo vent. Such controls are themselves well known in the art, and the particular form chosen is immaterial to the present invention.

The above described pump arrangement is intended primarily for use with an aircraft gas turbine. When in operation, normally both pumps 1 and 2 deliver their outputs additively to a common passage 30 through nonreturn valves 31a and 31b (see Figure 2). The two pumps being identically controlled, each pump Will deliver fuel at substantia ly equal rates, these rates being controlled by the angular position of the lever 14 as adjusted by the servo piston 27. In the event that one pump becomes seized, its drive shaft will break at its shear neck 1a or 2a, and it will be found that its track ring remains fixed in position. Movement of the servo piston 27 to vary pump output will then cause pivotal movement of the lever about the ball joint 12 or 13 of the fixed track ring (joint 12, if it is the pump 1 that ceased to function), the rod 19 carrying the lever fucrum moving axially against the loading of the leaf springs 23 so that the track ring of the operative pump (pump 2 in the assumed circumstances) may be adjusted by movement of the servo piston 27 to give the output desired. Movement of the lever in response to a given servo displacement is magnified, by reason of displacement of its fixed fulcrum, but this only compensates for the disablement of the one pump. In the case where one pump fails to deliver fuel but at the same time does not remain seized and does not lock its track ring in position, then adjustment of fuel output will take place by normal angular movement of the lever about its fulcrum, the serviceable oump delivering the whole output. It will be understood that the loading of the leaf springs to locate the lever fulcrum is such that it will withstand such differences of reactions applied by the two track rings and in this case the usual fulcrum 17 will remain fixed. The non-return valve 31a or 3111 in the output of the unserviceable pump through it.

- Whilst the invention has been described with relation "to radial cylinder variable stroke pumps itwillbe'appreciated that it is equally applicable to other kinds of variable stroke pump, e.g. swash plate pumps, hence the "term displacement control-asused herein is to 'be'read elements being shiftable in mutually oppositesenses for like control of the respective pumps, duct means common to the two pumps arranged to receive the output from each thereof during normal operation, a mounting element guided formovement in-a direction parallel to the direction of shiftingmovementof said control elements, spring-loaded means to retain said mounting element normally immovable in a fixed position, a lever pivotally mounted between its ends upon said mounting element and pivotally connected at its ends to the respective control elements, for rocking of the lever about itspivotal mount upon the fixedlypositioned mounting element to eifect conjoint and like but opposite move- ,ment of the control elements during normal operation,

the spring-loaded means being yieldable upon locking of either pumps control element to eifect control movement of the other pumps control element by rocking ofsaid lever about its pivotal connection to the locked control element as a fixed point, to correspondingly vary the position of the othercontrol element.

cludingaguide Whereinthe mountingelement is guided for rectilinear movement in the plane of rocking of the lever, and spring means reacting between said mounting element and its guide to retain the mounting element in its normal fixed position, but yieldable for rectilinear movement of the mounting element under the influence of a force precluding rocking alike but oppositely of the opposite ends of the lever.

3. A pressure liquid supply system as in 'claim 2, including a head uponthe mounting element, and leaf springs fixedly mounted by one end upon the guide and engaging the opposite faces of said head by their free ends.

4. A pressure liquid supply system as in claim 1, including a ball end and a bifurcated end straddling the corresponding ball end, and carried the one by each end of the lever and the other by the corresponding displacement control element.

5. A pressure liquid supply system as in claim v1,including a non-return valve interposed between the.out put of each pump and the common duct means.

References Cited in the file ofthis patent UNITED STATES PATETTS 2,458,985 Ferris Jan. 11, 1949 2,638,973 vCarey May19, 1953 2,772,755 Nallinger et a1. Dec. 4, 1956 2,799,138 Dornhofer July 16, 1957 2,804,016 Moore Aug. 27, 1957 

